Color screen with electron- and lightabsorptive material separating adjacent color strips



Dec. 14, 1965 P. RAIBOURN 3,223,872

COLOR SCREEN WITH ELECTRON- AND LIGHT-ABSORPTIVE MATERIAL SEPARATING ADJACENT COLOR STRIPS Filed Aug. 13, 1962 FIG. 3 I60) |6 INVENTOR Poul Roibourn M ATTORNEYS United States Patent T 3,223,872 COLOR SCREEN WITH ELECTRON- AND LIGHT- ABSORPTIVE MATERIAL SEPARATING ADJA- CENT COLOR STRIPS Paul Raibourn, Southport, Conn., assignor to Paramount Pictures Corporation, New York, N.Y., a corporation of New York Filed Aug. 13, 1962, Ser. No. 216,371 6 Claims. (Cl. 313-92) This invention relates to cathode ray tabues for the reproduction of color television images, and to methods of manufacture thereof. The invention provides such a tube characterized by an improved contrast ratio, by which is meant the ratio of brightness between portions of the tube screen which are impacted by cathode rays to represent white, and portions which are intended to be representative of no brightness.

The invention has particular applicability to cathode ray tubes for color television image reproduction wherein the screen includes a large number of narrow strips of phosphors luminescent on electron impact in plural primary colors, the strips being laid down in a repeating cyclic order, with the distance transverse of the length of the strips encompassing at least one strip of each primary color being of the order of magnitude of the color resolution desired to be provided. Especially the invention relates to such line-type tubes of the post deflection focus ing type, in which a focusing grid of linear conductors extending generally parallel to the length of the strips is disposed a short distance back of the screen toward the electron gun or guns of the tube, with at least one grid conductor being provided for each cycle of strips including at least one strip of each color. The grid coacts with an electron-permeable electrode overlying the screen on the gun side thereof to form a multiplicity of cylindrical electron lenses by means of which electrons of each cathode ray beam (if there are more than one) are focused between grid and screen to a spot at the screen of smaller cross-sectional area than the cross-section of the beam or beams as they arrive at the grid.

In accordance with the invention, an improved contrast ratio is obtained in such tubes by providing, between adjacent fluorescent strips on the screen, guard bands or separators of non-fluorescent, electron absorptive material. The guard bands may have a height as great as or greater than the width of the fluorescent strips which they separate. These guard bands prevent impact on the fluorescent strips of all electrons except those coming from well defined directions. They thus greatly diminish the diffuse illumination of the screen which results from cathode ray beam electrons which bounce off the focusing grid, from secondary electrons released at the grid by the impact of primary cathode ray beam electrons, and from cathode ray beam electrons or other electrons which strike the screen but bounce back therefrom, or expel therefrom secondaries which move part way toward the focusing grid and then fall back into the screen.

This reduction is due in part to the action of the guard bands in defining limited directions of approach from which electrons can reach the fluorescent portions of the screen between the guard bands. It is due also in part to the fact that the area on the screen occupied by the guard bands is non-fluorescent, so that electrons striking that area from whatever direction generate no light. Guard bands according to the invention also improve the contrast ratio by the reduction which they effect in the reflection back to the viewer of ambient light outside the cathode ray tube.

The invention will now be further described with reference to the accompanying drawings in which:

3,223,872 Patented Dec. 14, 1965 FIGURE 1 is a sectional view of a cathode ray tube according to the invention, wherein however no attempt has been made to show the guard bands and other detailed features of the screen on which the television picture is reproduced;

FIG. 2 is a fragmentary enlargement of that portion of FIG. 2 shown within the dash-line box 2 of FIG. 1, illustrating the construction of the screen in the tube of FIG. 1;

FIG. 3 is a fragmentary view similar to that of FIG. 2, illustrating however a modified form of screen construction according to the invention; and

FIG. 4 is a fragmentary sectional view of a temporary support for guard bands useful in the manufacture of cathode ray tubes in accordance with the invention.

FIG. 1 illustrates the application of the invention to a multi-gun color television tube of the bi-potential type disclosed in the copending application Serial No. 213,958 filed by applicant and others on August 1, 1962, which is assigned to the assignee hereof and which is entitled, Cathode Ray Tube. In such tubes, color selection is effected by allocating a separate electron gun to each of the primary colors, and the electrons are accelerated in their respective guns to a high potential from which they pass to a lower potential at a focusing grid before being reaccelerated between the focusing grid and screen in order to impact the screen at high velocity.

Specifically, the tube of FIG. 1 includes an envelope 1, a plurality of electron guns 4, 6 and 8, a target screen generally indicated at 10, and a focusing grid generally indicated at 12. The screen 10 includes fluorescent areas and guard bands as will be explained in further detail with reference to FIG. 2. There is indicated at 14 an electrode, which may take the form of a conducting ooating on the inside of the envelope, which extend-s from the location of guns 4, 6 and 8 along the tube axis 15 part or all of the way to the location of grid 12. The electrode 14 is fundamentally of tubular or, more specifically, of conical shape. It is connected to the electrode of highest potential in each of the guns, and surrounds the beams from all the guns in their flight towards the focusing grid. Its function is to extend to or towards the focusing grid the high potential condition to which the electron beams have been brought in the guns.

The guns, which may be of conventional construction, may have their electrodes of highest potential electrically connected together and to the electrode 14.

The grid 12 comprises a multiplicity of conductors 16 which extend substantially parallel to each other and to the surface to which the screen 10 generally conform-s, which surface may advantageously be substantially cylindrical in shape. In the drawings, these conductors extend perpendicular to the plane of the figures. The conductors 16 may be substantially uniformly spaced from each other and from the screen, and are electrically connected together by means not shown, and provided with a lead extending through the envelope. The space between each pair of adjacent grid conductors 16, and the area on the screen subtended thereby may for convenience be referred to as a cell.

The screen 10 includes an electrically conducting electrode over its surface (shown at 20 in FIG. 2), to which an appropriate potential may likewise be applied by a suitable lead-through, which may also be conventional and which is therefore not shown.

An exemplary set of operating voltages for the tube is approximately 25 kv. for the final accelerating potential in the electron guns, for electrode '14 and for the screen, and approximately 6 kv. for the conductors of grid 12.

The three guns 4, 6 and 8 may have their axes substantially in a plane perpendicular to the conductors 16, and inclined to each other in that plane at slight angles so I that, even upon a scanning of their beams across the area of the screen (as by conventional deflection coils, not shown) in a pattern of lines and frames, the beams from the guns are inclined to each other on entry into each cell. The directions at which, relative to each other, the beams of the guns approach the surface of the grid are indicated by the arrows 4', 6 and 8' in FIG. 2.

The result of the accelerating potential existing between the grid conductors and the screen (i.e., the coating 20 on the screen) is that each pair of adjacent grid conductors defines with the screen a cylindrical electron lens having a substantially line focus on the screen.

The resulting operation is illustrated in FIG. 2, where the reference characters 4", 6" and 8" identify the portions of the beams from guns 4, 6 and 8 entering the aperture between two adjacent conductors 16. The beams 4", 6 and 8" are seen to converge to separate line foci on the screen.

The screen includes a multiplicity of strips 22 of phosphors fluorescent in a set of primary colors, usually red, green and blue, These strips extend generally parallel to the length of the grid conductors =16 and are disposed in a repeating cyclic order, the width of the strips and their spacing being such that the distance transverse to the length of the strips which spans at least one strip of each primary color is of the order of magnitude of one picture element to be recreated with resolution as to color as well as brightness in the reproduced picture. On the screen, each cell includes, in the embodiment illustrated, one strip of each color, and the spacing of the grid wires is made such as to span one such cycle of strips 22.

In the tube of FIGS. 1 and 2 the strips 22 are laid down in the sequence XYZXYZ wherein X, Y and Z designate the three primary colors (e.g., red, green and blue) of the system of color television signals for whose reproduction the tube is intended, and the strips are so disposed with respect to the conductors of grid 12 that in each cell the strips of colors X, Y and Z are located at (and extend to either sideof) the line foci of electrons arriving from guns 8, 6 and 4 respectively.

As thus far described, the tube of FIGS. 1 and 2 may conform to the construction set forth in said copending application.

In accordance with the present invention however the strips 22 are laid down on a suitable transparent support, such as. the face plate portion 24 of the envelope 2, with a discrete, non-zero spacing between adjacent strips. These spaces are occupied by strips or ridges 26 of nonfluorescent material, preferably opaque to visible light, dark in color and made of a material of low atomic number such as carbon (e.g., in the form of graphite) to minimize the ejection of secondary electrons therefrom when impacted by cathode ray beam or other electrons having substantial energy. The ridge 26, sometimes termed guard bands, preferably have a height in directions generally parallel to that of the flight of electrons from gun to screen substantially greater than the height in the same direction or thickness of the strips 22. The height of the ridges 26 may thus be such'as to provide above each strip a, wall-enclosed space or groove 28 having a height A at least as great at its width B (FIGS. 2 and 3) Thus for example if the wires 16 are 0.003 inch in diameter and are spaced on centers by 0.040 inch, at a distance of 0.3 inch from the screen 10, the electrons entering the space between two adjacent grid wires 16 can be brought to a line focus having a dimension of the order of 0.002 or 0.003 inch transversely of the length of the strips 14, Each of the phosphor strips 22 may then be given a width of approximately 0.0067 inch and each of the opaque, inert strips 26 may be given a width ofapproximately 0.0067 inch. The relative widths of the phosphor strips 22 and inert strips or guard bands 26 may of course be different from that indicated by these figures.

In particular the guard bands may be wider than the phosphor strips, and may therefore occupy a larger fraction of the screen area than do the phosphor strips.

If the phosphor strips are 0.002 or 0.003 inch thick, the height of the guard bands 26 toward the grid 12 may be of the order of 0.010 inch.

The screen structure of the invention thus illustrated in FIG. 2 effects an important improvement in contrast ratio. In the first place, stray electrons reaching the screen are reduced in proportion to the fraction of the screen area occupied by the guard bands 26. Another factor contributing to improved contrast ratio is the absorption on the side walls 30 of the guard bands of electrons which, as strays, enter the spaces 28 at whose bottom the phosphor strips lie, but enter from the wrong direction. Thus for example if, as is desirable, the guard bands are, above the thickness of the phosphor strips, of greater height A than the width B of the spaces between them, the guard bands will prevent stray electrons having a substantial component of velocity transversely of the grid conductors from reaching the fluorescent strips. Such stay electrons include cathode ray beam electrons which strike the grid wires and bounce ofi of them, or secondary electrons ejected from the grid wires. Instead, the guard bands will confine fiuorescense at the strips 22 to the effect of electrons which approach the screen surface nearly perpendicularly, having trajectories close to the directions of the arrows 4', 6 and 8' in FIG. 2. Another factor contributing to improved contrast ratio is the action of the guard bands in absorbing a fraction of the light from the ambient room illumination which enters the face plate 24 of the cathode ray tube envelope 1, and which might otherwise be reflected at the inside surface of the face plate back towards the exterior of the tube. This fraction is substantially equal to the fraction of the screen surface occupied by the guard bands, The guard bands also improve the contrast ratio by reducing the effect of halation within the face plate 24 from light originating in the phosphor strips.

Another advantage of the screen structure of the invention is that the indented surface thereof promotes adhesion of the conductive coating 20, typically made of aluminum. This makes it possible to reduce the spacing between the screen and grid, one of the limiting factors on reduction of this spacing being the tendency of the coating to pull off of the screen under the electrostatic stress existing between the coating and grid.

FIG. 3 illustrates another embodiment of the cathode ray tube of the invention, differing from that described in detail in conjunction with FIG. 2 in that in place of the strips 22 of materials fluorescent on electron impact in the colors X, Y and Z, there are employed in all of the spaces between guard bands strips 32 of material fluorescent in white upon electron impact. Between each of these fluorescent strips and the face plate of the tube envelope there is disposed a strip 34 of glass or other translucent or transparent material, and the strips 34. are transmissive from space to space in the colors X, Y and Z.

In accordance with the invention the guard bands may be deposited on the face of the cathode ray tube, especially if the face plate is of cylindrical shape, from a temporary supporting sheet, for example of nitrocellulose material, having a pattern of grooves in one surface thereof, which grooves are filled with graphite in a suitable binder. These grooves conform in dimensions and relative position to the guard bands desired to be produced. Such a sheet is shown in fragmentary cross-section at 40 in FIG. 4, with strips 25 of graphite and binder therein. In the manufacture of a cathode ray tube according to the invention, before assembly of the face plate to the remainder of the envelope the sheet 40 is positioned against the inside surface of the face plate, in a location accurately defined in terms of indexing marks or features which also define the position which the focusing grid and its conductor wires will have in the finished cathode ray tube. The face plate and sheet 40 are then heated in a suitable atmosphere, causing the nitrocellulose sheet to evaporate and leaving the graphite strips 25 adherent to the face plate.

The nitrocellulose sheets may be made by casting on a suitably grooved copper or other metallic plate having a correct pattern of grooves on its surface. To make such a plate, a pattern of opaque bands may first be laid down at the positions of the desired guard bands in a cathode ray tube whose face plate is coated on the inside with an electron sensitive photo resist material. To form the pattern of bands, one or more electron beams are scanned over the target surface within which the bands are to be produced, in such a fashion as to expose to electron bombardment that part of the target surface (which is coated with the photo resist material) which the bands are to occupy. A wobbling supplementary deflection voltage may be employed in order to produce bands of the desired Width. In a development process the portion of the coating, not impacted may be removed, to leave a set of opaque strips or bands at the location of the desired guard bands. This process, sometimes referred to as electron printing, is described in my copending application Serial No. 833,266 filed August 12, 1959.

A photographic image may then be formed of the electron printed set of bands, and the grooved copper or metallic plate on which the supporting sheets such as that shown at 40 in FIG. 4 are cast may then be manufactured from such a photographic image by the methods of photolithography.

While the material of which the guard bands is made has been described hereinabove as being electron absorptive, it is preferably light absorptive as well.

Attention has been called herein to the fact that these guard bands improve the contrast ratio by the reduction of reflection back to the viewer of the ambient light shining on the cathode ray tube screen and of the light from the image itself which is internally reflected from the outer surface of the tube envelope. This effect he comes very important for a single gun monochrome tube or for a multi-gun color tube. In such a case, under the conditions normally obtaining in a black-and-white tube of a white highlight brightness of eighty foot lamberts or a bipotential post deflection focusing tube with a white highlight brightness of two hundred to four hundred foot lamberts, these brightnesses are expressed as the brightnesses integrated over the entire surface. In a usual cathode ray tube of the shadow-mask color or of the monochrome variety, the picture is seriously affected in its quality by a ambient illumination of twenty-five foot lamberts or over due to the reflection back to the viewer of a great portion of this ambient illumination. However, under the conditions hereinabove mentioned of a phosphor width of .003 inch, there could be black guard bands, which would absorb this ambient light, of a width of .031 inch per 3 unit color cell of .040 width. In such a case only 4 of the ambient illumination would be reflected.

It has been found by experiment that a white highlight brightness of a television image of 200 to 400 foot lamberts is sufiiciently bright to maintain a satisfactory and pleasing picture under almost all conditions of daylight viewing and in artificially lighted display rooms. Under these conditions, the brightness of a matte or partially matte white surface is usually near twenty-five and almost always under fifty foot lamberts. At such ambient brightness levels present color sets on the market do not yield a satisfactory and pleasing picture.

To obtain a white highlight brightness of approximately three hundred foot lamberts on a three-gun bipotential post deflection color cathode ray tube requires a screen and gun anode voltage of 25,000 volts. However, on a tube such as has been described with the above parameters and guard bands of .030 per cell, this means a white highlight brightness for the illuminated portion of the screen of 40/9 x 300:1333 foot lamberts. It also means that only, at the most W of the incident ambient illumination is reflected to the eye, or under the conditions just described of normal ambient illuminations of 25 foot lamberts, that a general illumination of not more than M x 25 =5 .625 foot lamberts is reflected to the observer. This amount when compared with the brightness of 1333 foot lamberts appears to be of almost no consequence.

It thus appears that, by a combination of a bipotential post deflection cathode ray tube and guard hands, a television picture will be available which would be useful even in direct sunlight at 25,000 volts on gun and screen and for all shaded conditions at much less voltages, thus avoiding all questions of voltage protection and X-ray generation.

While the invention has been described in terms of a number of preferred embodiments, the scope of the invention itself is set forth in the appended claims.

I claim:

1. A cathode ray tube for the reproduction of color television images comprising a target for cathode rays, a multiplicity of strips of phosphors fluorescent in plural primary colors disposed one adjacent another on said target in a repeating cyclic order, and electron absorptive, non-fluorescent spacing means separating each two adjacent ones of said strips, said spacing means having a height above said strips greater than the width of said strips.

2. A cathode ray tube for the reproduction of color television images comprising a target for cathode rays, a multiplicity of strips of phosphors fluorescent in plural primary colors disposed one adjacent another on said target in a repeating cyclic order, and electron absorptive non-fluorescent, light absorptive spacing means separating each two adjacent ones of said strips, said spacing means having a height above said strips greater than the width of said strips.

3. A cathode ray tube for the reproduction of color television images comprising an electron gun, a target spaced from said gun across which a beam of cathode rays from said gun is adapted to be bi-dimensionally deflected, a focusing grid of substantially parallel conductors interposed between said gun and target, a multiplicity of substantially parallel strips of phosphors fluorescent in plural primary colors disposed side-by-side on said target substantially parallel to said conductors in a repeating cyclic order, and electron absorptive, nonfluorescent spacing means separating each two adjacent ones of said strips, said spacing means extending from said target toward said gun a distance at least as great as the width of said strips.

4. A cathode ray tube for the reproduction of color television images comprising a plurality of electron guns, at target spaced from said guns across which a beam of cathode rays from each of said guns is adapted to be bi-dimensionally deflected, a focusing grid of substantially parallel conductors interposed between said gun and target, a multiplicity of substantially parallel strips of phosphors fluorescent in plural primary colors disposed sideby-side on said target substantially parallel to said conductors in a repeating cyclic order, and electron absorptive, non-fluorescent spacing means separating each two adjacent ones of said strips, said spacing means extending from said target toward said guns a distance at least as great as the Width of said strips.

5. A cathode ray tube for the reproduction of color television images comprising a plurality of electron guns, a target, a focusing grid of parallel linear conductors intermediate said gun and target, a multiplicity of substantially parallel strips of phosphors fluorescent on electron impact in plural primary colors disposed on said target substantially parallel to said conductors in a repeating cyclic order, at least one said conductor being provided for each cycle of said strips, the width of said cycle and the spacing of said conductor being less than the distance from said conductors to said target, and electron absorptive, non-fluorescent, light absorptive spacing means separating each two adjacent ones of said strips, said spacing means extending past the surface of said strips, in directions substantially parallel to the path of electrons from said gun passing from said grid to said target, to a height greater than the width of said strips.

6. A cathode ray tube for the reproduction of color television images comprising a plurality of electron guns, a target over which a beam of electrons from each of said guns is adapted to be bi-dimensionally deflected, a focusing grid of parallel linear conductors intermediate said gun and target, a target electrode overlying said target on the side thereof adjacent said guns, said target electrode being substantially coextensive with said target, a tubular electrode surrounding the beams from said guns and extending from said guns at least part way towards said grid, a multiplicity of substantially parallel strips of phosphors fluorescent on electron impact in plural primary colors disposed on said target substantially parallel to said conductors in a repeating cyclic order, at least one said conductor being provided for each cycle of said strips, the width of said cycle and the spacing of said conductors being less than the distance from said conductors to said target, and electron absorptive light absorptive non-fluorescent spacing means separating each two adjacent ones of said strips, said spacing means extending past the surface of said strips, in directions substantially parallel to the paths of electrons from said guns passing from said grid to said target, to a height greater than the width of said strips.

References Cited by the Examiner UNITED STATES PATENTS 2,614,231 10/ 1952 Lawrence.

2,705,765 4/ 1955 Geer.

2,751,516 6/1956 Lawrence.

2,837,687 6/ 1958 Thompson et al.

2,842,697 7/ 1958 Bingley.

2,847,596 8/1958 Felburg.

2,996,634 8/1961 Woodcock 31392 3,037,419 6/1962 Nixon 178-7.85

3,041,456 6/1962 MacLeod 313-92 X FOREIGN PATENTS 810,110 3/1959 Great Britain.

GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner.

C. O. GARDNER, R. SEGAL, Assistant Examiners. 

1. A CATHODE RAY TUBE FOR THE REPRODUCTION OF COLOR TELEVISION IMAGES COMPRISING A TARGET FOR CATHODE RAYS, A MULTIPLICITY OF STRIPS OF PHOSPHORS FLUORESCENT IN PLURAL PRIMARY COLORS DISPOSED ONE ADJACENT ANOTHER ON SAID TARGET IN A REPEATING CYCLIC ORDER, AND ELECTRON ABSORPTIVE, NON-FLUORESCENT SPACING MEANS SEPARATING EACH TWO ADJACENT ONES OF SAID STRIPS, SAID SPACING MEANS HAVING A HEIGHT ABOVE SAID STRIPS GREATER THAN THE WIDTH OF SAID STRIPS. 